Extrusion of thermoplastics



Dec. 29, 1953 c. E. SLAUGHTER EXTR'USIQN OF THERMOPLASTICS 2Sheets-Shoat 1 Filed Dec. 12, 1950 FIGJ FIG

lNVENTOR CHARLES E. SLAUGHTER 7 F l G. 5

AT 'i'OR NEY Dec. 29, 1953 Q SLAUGHTER 2,663,904

EXTRUSION OF THERMOPLASTICS Filed Dec. 12, 1950 2 Sheets-Sheet 2 FIG. 8

INVENTOR CHARLES E. SLAUGHTER ATTORNEY Patented Dec. 29, 1953 2,663,904nxrnusron or THERMOPLASTICS' Charles E-.- Slaughter, New Canaan, Conn;as-

signor to Extruded Plastics, Inc., a corporation f of ConnecticutApplication December 12, 1950, Serial'No. 200,344- 8 Claims. (01. 18-44)1 This invention. relates to'synthetic resinous tubing of substantiallyuniform character and. to methods and machines: for making. the same;

In the extrusion of thermoplastic tubing considerable difficulty hasbeen experienced in the production of such tubing of largeinternal boreor diameter and also in cases of smaller. diameter tubing where thewanof the tube is insufficient in thickness to prevent collapse durinthe course of manufacture. For example, inone method, of extrusion, thetubing from the regular extrusion die is passed directly into awaterbath set at a predetermined temperature, which bath exhibits twodifferent effects on" the tubing. The low temperature of the watercompared with that of the hot plastic, liar-dens itto' a predeterminedshape and so prevents collapse of th'e tubing from the effect of gravityi- At the same time, however, the pressure exertedby the water tends tomake the tubing collapse since the external pressure, duetothe-surrounding water, is" greater than the internal pressure.

In small diameter tubing, as for instance, 1 inch 0. D; with a men wall,or even in the larger diameter tubing, such as inch but with avery smallbore; as-forinstance, inch bore, the pressure exerted by the water isinsufiicient to cause deformation; but in the thinner walls, especiallyin the larger diameters, thiscollapse' is very serious. To overcome thisexternal water pressure, it is necessary to balance the internalpressure exactly against the external pressure.

One expedient to balance these pressures is to extrude the tubingvertically into'water or other coolant while blowing air through thecore of the die to balance the: column of Water around the tube. Thisexpedient requires expensive installation sinceit isrnecessary toextrude from a height of not less-than 20 feet in order to obtain astandard commercial. 12 foot length, and in addition the problem ofcutting ofi to length is very difiicult since this must becarried outwhile the tubing is submerged to a depth. of 8 or 10 feet.

A further. expedient which may be used with very flexible types ortubing, such as polyvinyl resins, etc., consistsofsealing' the tube andblowing air into it. Whenit is necessary to cut the tubing tolength; thetub'ei is rescaled just before the cut. This is most unsatisfactory asit is impossible to control the air pressure exactly and further, thisprocess is not commercially possible .on the rigid types ofresins, suchas the Sty-'- renes, acetate" buty-r'at'es; unplast-icized 'vinyn, etc.

Nor" has it proved. particularly satisfactoryto seal the end of the.tube with a stopper such as a rubber cork provided. with a small. holecut through its-length to; permit a small stream: of air to passthrough, whileat the same time building up suflicient back pressure sothat the internal pressure exerted by the-air andtheexternal pressureexerted by thewater' arebalanced. Even with this expedient the tubingcannot be cut 2 without causing a collapse, which collapse while not soserious in the smaller diameter tubing, involvin a Waste of a few feetof misformed tubing, is so serious withlargerdiameter tubing such as .1-inch and above, that the process is uneconomical.

In suchtubing where the ratio of wall thickness tointernal bore isinsufficient to prevent collapse of thetubing' when the resinousmaterial isiin plastic condition duringatheextrusion process orto-prevent substantial variation in external diameter from a givenpredetermined size, .diificulties are encountered. For example, even. insmall diameter tubing of say inch 0. D. x: inch I. D. it has not been:possible to maintain the desired tolerances in diameter. In larger sizetubing, as for example, one inch in diameter and above, thedifi'iculties were insuperable and no such large size tubing hasheretofore been made.

Among the objects of the present invention is the production of extrudedsynthetic resinous tubing of substantial uniformity throughout itslength.

Further objects include the production of such tubing of large sizediameter.

Further objects and advantages of the present invention will appear fromth more detailed description set'forth below, it being understood thatthis more detailed description is given by way of'explanationandillustration only, and not by way of limitation, since various changestherein may be made'by those skilled in the art without departin fromthescope and spirit of the present invention.

In connection with that more detailed description, there is shown in theaccompanying drawmg, 1n

Figure 1, an elevation, partly in section, illustrating onedevice thatmay be employed in accordance with the present inventiomin Figure 2, adetail of'a floating plug shown in Figure 1; in

Figure 3', a modified form of apparatus that can be utilized inaccordance with the present invention; in'

Figure 4, a further modification of apparatus that can be employed incarrying out the present invention; in

Figure 5, asection-through a cross-head type of extrusion machineutilized in accordance with the present invention in Figure 6, a sectionthrough a cross-head type of extrusion machine'using a porous mass as afloating plug; in

Figure 7, a section through extruded tubing illustrating-a furthermodification of the invention; and in.

Figure 8, a still; further modified form of ap aratus.

In accordance with the present invention extruded synthetic resinoustubing is produced in continuous lengths of uniform cross-sectionmaintained within close tolerances, particularly where the ratio of wallthicknessfof thetubing to its internal bore is insufficient to preventcollapse of the tubing when the resinous material is in plasticcondition during the extrusion process. Tolerances within limits ofplus, or minus one-half of one per cent are readily maintained by thepresent invention. In small size tubing this will be less than .005 inchand tubing may be readily produced which does not vary in crosssectionthroughout the length of the tubing more than from .001 inch to .002inch. Such tubing, for example, may be of a size inch 0. D. x A; inch I.D. and in lengths of 1000 feet. The invention is particularly useful inthe production of uniform thin walled tubing of at least inch I. D. andspecifically above inch 0. D. There is also included large diametertubing of 1 inch or more diameter running to 3 inches in diameter andhigher.

In accordance with the present invention, collapse of tubing of extrudedthermoplastic type while in non-self-sustaining plastic condition, isprevented by introducing a fluid such as air within the tubing, and thefluid pressure is maintained substantially uniform to obtain tubing heldto close tolerances. The pressure is maintained during extrusion andcooling desirably between the points of extrusion and cutting either bya floating plug or by a porous or semipermeable mass anchored inposition in the tubing or in other ways.

As illustrated in Figure l, the extruded thermoplastic tubing I afterextrusion from the usual extruding die (not shown) and immersion in acooling bath such as water (not shown), is received on the belt conveyorB. The usual means (not shown) is utilized for introducing fluidpressure such as air pressure, within the tube 1 by appropriate meanswithin the die, as through a cross-head.

A plug 2 is floated within the tubing I at some convenient positionbetween the points of extrusion and cutting and may be maintained withinthe tubing l by being anchored by the strand 3 to a magnetizable core 4.A solenoid 5 of annular cross-section has a central opening 6 withinwhich the extruded tubing I may pass freely, electrical connections Ibeing provided for the solenoid 5. The core 4 may consist of a number oflengths of Swedish iron wire 8, held together by bands 9, one of thewires such as H! extending beyond the core and connected to the strand 3to which the plug 2 is attached.

Desirably the plug 2 consists of a number of woolen strands II.

Strands of wool may desirably be used for the pedients, so long as afloating pug: is maintained within the tubing'to retain the necessarypressure to prevent collapse of the tubing. The method and meansillustrated may be utilized in producingtubing of any desired internalbore or diameter and for the first time makes it possible toextrude-thermoplastics, particularly synthetic resinous tubing ofrelatively large internal diameter, such as '1 inch, 1 inch and larger.If desired, particularly in the case of the larger size extruded tubing,or in event where desired, several floating plugs may be positionedwithin the tubing at any desired points.

It is desirable to place the plug for maintaining the pressure withinthe tubing, at a substantial distance from the extrusion die since inthis way, there is provided acomparatively large volume of entrapped airbetween the point of extrusionand the point where the plug ispositioned, and this comparatively large volume of entrapped air withinthe tube acts as an air cushion and takes up any minor variation in airpressure that may occur through minor changes in inside diameter or anyother changes which give rise to fluctuations.

In the form of device illustrated in Figure 3, in lieu of utilizing awoolen strand tail or plug as illustrated in Figures 1 and 2, there isillustrated a device inwhich a solid plug is utilized both for thepurpose of maintaining the desired fluid pressure within the tubingduring extrusion, and also to control the size of the tubing producedvery closely.

Desirably the tubing may be reheated at any pre-determined length fromthe die and the plug used at that point, in order to provide an adequateair cushion. The plug in these instances may be a cylindrical rod, ball,or any other shape desired, desirably of non-magnetic material attachedas a tail to the laminated iron core. Means for permitting a stream ofair to pass the plug is desirably provided. As shown in Figure 3, a ball32 is employed, having the desired diameter. By utilizing a sufficientlystrong magnetic field, the extruded tubing is pulled over the ball 32and expanded by a few thousandths of an inch to obtain the true internalbore desired.

tail or plug 2 as it has been found that the static electricitygenerated by the plastic traveling over the rubber conveyor belt, holdsthe strands of wool in contact with the internal surface of the plasticand permits internal pressure of the fluid or air to be maintainedwithin close limits such as plus or minus one inch of water pressure.

The plug or tail 2 may thus be said to float within the tubing I whilethe latter is being carried forward by the conveyor belt B and yetefiectively seals the fluid pressure within the extruded tubing I sothat when the tubing passes to the cutting or shearing element M thepressure is maintained within the tubing while it is being extruded andprevents any collapse.

The form of device, and means for floating the plug or tail within thetubing, including the tail itself of woolen strands, the solenoid, andthe core may be replaced by other means and ex- In the modificationshown in Figure 4, the plug is shown as of magnetizable material whichis maintained in position by the solenoid, for the purpose of retainingthe necessary fluid pressure within the tubing i. In this case the plugconsists of magnetizable material, for example, in the shape of acylinder 44 having a perforation, the cylinder floating within thetubing 1 maintained in position by the solenoid '5. Here again as in thedevice of Figure 3, the machine of Figure 4 is employed at a point wherethe tubing is semi-plastic so that the plug serves not only to maintainthe air pressure in the tubing 1, but also to shape the internal bore ofthe tubing to the true bore desired.

The standard type of extrusion machine of the cross-head type may bemodified for use in accordance with the present invention and othermeans for positioning the floating plug may be employed as shown inFigure 5. Such machines are particularly useful in the production oflarge diameter tubing to secure a more even flow of material around thecore in the die. As shown in Figure 5, the tube 5! is extruded from thedie 52 into which the plastic material is fed by the worm 53 around thecore 54, a centrally placed orifice or opening 55' permitting theintroduction of air to support the tube. during extrusion. While afloating plug. of. anyidesired type. as illustrated in Figures. l-i may.beutilized as ex; plained hereinabove, other. expedients. may. beutilized. Thus a wire 56 may be attached to the die 52 at any desiredpoint 5'6 and threaded through the opening 55 in thecoreie, the. wireextending forwardly into the tube 5| carried on belt 57, and a floatingplug 58 as shown anddescribed in Figures 1 and 2 attached to 'the wire56 to 59. The air pressure in the tube is sufli: cient in conjunction.with the extruding operation to maintain the plug in 'desiredp'ositionfor its function as set forth above. The apparatus of Figure 5 will thusfunction exactly inTthe Way described above for Figure 1 to producelarge diameter tubing of uniform. size maintained within close range oftolerances.

The type of floating plug'illustrated in Figure 5 attached to a wirerunningto the diemay be utilized in any of the machines such' as thoseillustrated in Figures 1, 3 and 4 in lieu. of. the V magnetic means formaintaining the floating plug in position. W

While the core 4 has been set forth aboveto be produced of Swedish ironwire, it may be made of any desirable magnetizable material, as

for example, Alnico, etc. Whereas in the structure shown in Figure 4,the core 44 is itself utilized as the floating element, and that core issubjected to a solenoid or other magnetizing means to retain it inposition, the material of which the floating element 44 is composed,should be of such nature, that it does notadhere so tenacious'ly to theextruded tubing being formed, asto be withdrawn from its position withinthe magnetic field created by the solenoid] Mate? rials like brass orstainless steel may desirably be employed. 5

In connection with th type ofmaterial used for such elements it may alsobe pointed out that such choice of material may depend on the expedientemployed for maintaining the floating plug in position. As illustratedherein, a sole, noid has been employed to produce a magnetized fieldwhich acts on the mandrel or core' to hold it in position. However, thisis illustrated only for purposes of explanation and exemplificati'on andany other means may be employed in this connection to hold thepl'ug'inposition within theextruded tube. Thus it; is possible to utilize eddycurrents or to use inducedcurrents to float a desired plug or devicewithin the 'extrudedtube for these purposes and thefchoice or materialfrom which the floating element is produced will depend on the exactconditions under which such element is employed.

In connection with the core described-herein, it may be pointed out thattheeddy currents from the solenoid. described herein create asubstantial amount of heat if the core is not laminated.

Bythe methods and means herein. set. forth, it is possible to extrudethermoplas c tub n Da tic ularly of synthetic resinous character, oftrue bore within a tolerance of one-half of one per cent by continuousextrusion frnethods ayoiding any collapse of the tubing during suchmanufacture even when out in any desired predeter- 1 mined length, suchas standard'lz foot length. Extruded tubing of any.v desiredcross-section may be produced such as circular, oval, elliptical,square, hexagonal, etc.

Instead of using floating plugs ofi-substam tially solid character asillustrated above, the plug may be. made 6f a porous mass or semipermeable material such as sponge rubber anchored in position byany ofthemeans set. forth above between the die and the cutting offapparatus,the mass. beingsumciently porous to permit taking up slightvariations.or permitting adjustment to. slight. variation. in the. internaldiameter of the tubing. being extruded. Figure 6 illustratestheutilization of a plug of this character. As there shown, a wire or otherattaching means. 66may be. attached to the die. 62 at any desired pointsuch as 6.6. and threaded through the opening. 65 in the.- core 54,. theWire extending forwardly into the tube 6t carried on belt 67 andafloating plug 68= attached to the wire 66 at-BB. The-fluid pressureinthe tube is. sufiicient inconjunctionwith theextruding op, eration tomaintain-the plug anchored in, the desired position for its function as.set. forth above. The plug 68;may. beof sponge rubberor other porousmaterial or. semi-permeable sub-.- stance which will maintain asubstantially uniform air orfiuid pressurein thetubing, themass beingsufficientlyporous to. permit. adjustment to slight variations in theinternal. diameter of the tubing.

Asillustrative of. othenmethods; that may be utilized in lieu offloating plugs, reference maybe made to Figure 7. Inthi's case theextruded tubing H is given a bend as; illustrated at to form. a. trapwithin which. aliquid such asmercury 13 may be introduced to. formanairlock. In. long lengthsof tubing, the tubing itself. willv bowsuflicientl-y to form the a trap. The-tubing is cut beyond the trap ata-point such asthat indicated at 14.

The liquid trap, illustrateddnf'igurei may also. be used in conjunction.with.-.anyot the plugs shownabove. For example any. ofa-the plugs ordevices. ofFigures 11 to- 6 inclusive may. be used" and in additiona-trap .holding liquid as shownin Figure 7 be employedsimultaneouslywith the; plugordevice of Figures-1 to 6. Ordinarily bothare notnecessary, butv in someiinstances may be desirably. employed to obtainthe: added effect.

. Thusasshownin.Figurefiythetubing I may car ry-a. plug H asshownin-Figur.e: 1 andalsothe tubing may haveia bendlz to 'form a trapwithin-which the liquid ltzfo'rmsan air lock, the tub ing being outbeyond: the rap as at 74 Any desired thermoplasticmaterials-- maybeutilized in theproduction-cf such; extruded tub ing. in accordance.withthe present invention, particularly synthetieresinous: materialssuch. ascellulose derivativesincluding the-esters, particularlycellulose acetate and" oellulose acetate butyrate; and the celluloseothers such as ethyl cellulose; polymerized vinyl materials such aspolymerized vinyl' acetate, styrenes, and other thermoplastic andresinous compositions. that may. be. extruded incontinuous-lengths,includingthe vinyl resins and-nylon typeresins.

Thereis an outstanding -advantage-- in the use of the invention-inmaking longlcoils of tubingof; for:- example, relatively sm allidiameter such suchconditions, the volume of:- airthat leakedi past thedevice wasso insignificant; that there- While the invention has beenparticularly illustrated in connection with the production of syntheticresinous tubing by extrusion methods, it may be utilized in connectionwith other materials and may be employed in the extrusion, particularlywhere continuous lengths of such products are to be obtained.

, This application is a continuation-in-part of Serial No. 487,403 filedMay 17, 1943, now abandoned, entitled Synthetic Resinous Tubing.

Having thus set forth my invention, I claim:

1. The method of manufacturing thermoplastic tubing of fixed bore byextrusion which comprises extruding thermoplastic unconstrained tubingin non-self-sustaining plastic condition, introducing a fluid within thetubing during extrusion to prevent collapse of the unconstrained tubing,maintaining the pressure of the fluid within the unconstrained tubingsubstantially uniform, cooling the tubing to a temperature at which itis self-sustaining, the pressure being maintained by liquid trapped inthe extruded tubing at a point where it is self-sustaining.

2. The method of manufacturing thermoplastic tubing by extrusion whichcomprises extruding thermoplastic tubing in nonself-sustaining plasticcondition, introducing a fluid within the tubing during extrusion toprevent collapse of the tubing, cooling the tubing to a temperature atwhich it is self-sustaining, cutting the extruded cooled tubing to apredetermined length, and maintaining the pressure of the fluid withinthe tubing substantially uniform during the operation set forth byliquid trapped in the tubing at a point where it is self-sustaining andby floating a plug within the tubing at a point removed from the pointof extrusion and before the point of cutting, to maintain a cushion offluid in the tubing of substantially uniform pressure.

3. The method of manufacturing thermoplastic tubing by extrusion whichcomprises extruding thermoplastic tubing in non-self-sustaining plasticcondition, introducing a fluid within the tubing during extrusion toprevent collapse of the tubing, cooling the tubing to a temperature atwhich it is self-sustaining, cutting the extruded cooled tubing to apredetermined length, and maintaining the pressure of the fluid withinthe tubing substantially uniform during the operation set forth byliquid trapped in the tubing at a point where it is self-sustaining andby floating a metal plug within the tubing between the points ofextrusion and cutting and anchoring the plug in position by a wireextending from the plug through the tubing to the extrusion means.

4. The method of manufacturing thermoplastic tubing by extrusion whichcomprises extruding thermoplastic tubing in non-self-sustaining plasticcondition, introducing a fluid within the tubing during extrusion toprevent collapse of the tubing, cooling the tubing to a temperature atwhich it is self-sustaining, cutting the extruded cooled tubing to apredetermined length, and maintaining the pressure of the fluid withinthe tubing substantially uniform during the operation set forth byliquid trapped in the tubing at a point where it is self-sustaining andby floating a porous mass within the tubingbetween the points ofextrusion and cutting, the mass being sufflciently porous to permitadjustment to slight variations in the internal diameter of the tubing.

5. Apparatus for manufacturing thermoplastic tubing of fixed bore byextrusion which comprises means for extruding thermoplasticunconstrained tubing in non-self-sustaming plastic condition,

means for introducing a fluid within the tubing during extrusion toprevent collapse of the unconstrained tubing, means for maintaining thepressure of the fluid substantially uniform within the unconstrainedtubing, and means for cooling the tubing to a temperature at which it isself-sustaining, the pressure maintaining means including liquid trappedin the extruded tubing at a point where it is self-sustaining.

6. Apparatus for manufacturing thermoplastic tubing by extrusion whichcomprises m ans for extruding thermoplastic tubing in non-selfsustainingplastic condition, means for introducing a fluid within the tubingduring extrusion to prevent collapse of the tubing, means formaintaining the pressure of the fluid substantially uniform within thetubing, means for cooling the tubing to a temperature at which it isself-sustaining, and means for cutting the tubing to a predeterminedlength, the pressure maintaining means including liquid trapped in thetubing at a point where it is self-sustaining and a floating plugowithinthe tubing between the points of extrusion and cutting, to maintain acushion of fluid in the tubing of substantially uniform pressure.

7. Apparatus for manufacturing thermoplastic tubing by extrusion whichcomprises means for extruding thermoplastic tubing innon-self-sustaining plastic condition, means for introducing a fluidwithin the tubing during extrusion to prevent collapse of the tubing,means for maintaining the pressure of thefluid substantially uniformwithin the tubing, means for cooling the tubing to a temperature atwhich it is self-sustaining, and means for cutting the tubing to apredetermined length, the pressure maintaining means including liquidtrapped in the tubing at a point where it is self-sustaining and afloating metal plug within the tubing between the points of extrusionand cutting to maintain a cushion of fluid inthe tubing of substantiallyuniform pressure, and means extending from the plug through the tubingto the extrusion means to anchor the plug in position.

8. Apparatus for manufacturing thermoplastic tubing by extrusion whichcomprises means for extruding thermoplastic tubing innon-self-sustaining plastic condition, means for introducing a fluidwithin the tubing during extrusion to prevent collapse of the tubing,means for maintaining the pressure of the fluid substantially uniformwithin the tubing, means for cooling the tubing to a temperature atwhich it is self-sustaining, and means for cutting the tubing to a,predetermined length, the pressure maintaining means including liquidtrapped in the tubing at a point where it is self-sustaining and aporous mass anchored between the extrusion means and the cutting means.

CHARLES E. SLAUGHTER.

References Cited in the flle of this patent UNITED STATES PATENTS NumberName Date 2,047,554 Fischer July 14, 1936 2,337,927 Reichel et al. Dec.28, 1943 2,433,937 Tornberg Jan. 6, 1943 2,461,976 Schenk Feb. 15, 1949FOREIGN PATENTS Number Country Date 3,999 Great Britain July 25, 1891

